1. Field of Invention
The present invention relates to a liquid crystal display device and an electronic device, and, more particularly, to a structure of a transflective liquid crystal display device which makes it possible to increase luminance in a direction of a line of sight of a user.
2. Description of Related Art
A reflective liquid crystal display device consumes little power because it does not have a light source such as a backlight, and has, from the past, been frequently used in various portable electronic devices, accessory display sections of devices, or the like.
However, since a reflective liquid crystal display device performs a displaying operation using outside light such as natural light or illumination light, it has a problem in that it is difficult to visually recognize what is displayed in dark places. To overcome this problem, there has been proposed a form of a liquid crystal display device which makes it possible to visually recognize what is displayed by using outside light in bright locations similarly to an ordinary reflective liquid crystal display device, and by using a light source disposed inside the display device in dark places. In other words, this liquid crystal display device uses displaying methods of both a reflective type and a transmissive type, so that, by switching a display mode to either a reflection mode or a transmission mode display type in accordance with the surrounding brightness, it is possible to provide a clear display even if the surrounding is dark while reducing power consumption. Hereunder, in the specification, this type of liquid crystal display device will be referred to as “transflective liquid crystal display device.”
As one form of the transflective liquid crystal display device, a liquid crystal display device having the structure shown in FIG. 10 has been proposed. In a liquid crystal display device 200 shown in FIG. 10, liquid crystal 203 is sandwiched between a pair of upper and lower transparent substrates 201 and 202; a reflective polarization layer 204 and an insulating layer 206 are placed upon each other on the lower substrate 201; a stripe-shaped scanning electrode 208, formed of a transparent electrically conductive film formed of ITO or the like, is formed thereupon; and an alignment layer 207 is formed so as to cover the scanning electrode 208. On the other hand, color filters 209 are formed on the upper substrate 202; a planarizing film 211 is formed thereupon; and signal electrodes 212, formed of transparent electrically conductive films formed of ITO or the like, are formed on the planarizing film 211 in the form of stripes in a direction orthogonal to the scanning electrode 208; and an alignment layer 213 is formed so as to cover the signal electrodes 212. A forward scattering plate 218, a retardation film 219, and an upper polarizer 214 are disposed outwardly of the upper substrate 202 in that order from the upper substrate 202. A backlight 217 is disposed at the bottom surface side of the lower substrate 201.
Here, FIG. 11 is a side sectional view partly showing the reflective polarization layer 204 and the lower substrate 201 shown in FIG. 10. As shown in this figure, the reflective polarization layer 204 has a structure formed by stacking dielectric interference films 204a having the shape of a prism having a triangularly wavy form in cross section. For example, an Si layer and an SiO2 layer are alternately stacked (three layers in FIG. 11) at a pitch of the order of 5 μm.
In the liquid crystal display device 200 having the above-described structure, when a displaying operation is performed in a reflection mode, light incident upon the display device 200 from above the upper substrate 202 passes through the liquid crystal 203 from the upper substrate 202 and reaches the reflective polarization layer 204. The light is reflected by the reflective polarization layer 204 and returns towards the upper substrate 202, so that the displaying operation by reflection is carried out. When a displaying operation is performed in a transmission mode, light is emitted from the backlight 205, and, of the portions of the light that have passed through the lower substrate 201, the portion of the light that is parallel to a polarization axis of the reflective polarization layer 204 passes therethrough and is used for the displaying operation.
Accordingly, according to the above-described liquid crystal display device 200, when outside light or light of the backlight 217 is used for the displaying operation, conversion from circularly polarized light to linearly polarized light or conversion from linearly polarized light to circularly polarized light does not occur, so that there is no loss of light caused by the conversion, thereby making it possible to provide a relatively bright display.
However, it has been found that although the above-described liquid crystal display device has high reflectivity, it does not provide a very bright display in the reflection mode. Therefore, the inventor has examined at length the state of reflection of light at the reflective polarization layer 204 in the liquid crystal display device 200, and has found out the following. More specifically, the reflective polarization layer 204 has the shape of a triangularly wavy prism as shown in FIG. 11. In the reflective polarization layer 204, two types of inclined surfaces 204A and 204B are alternately formed at regular intervals. The angle between each of these two types of inclined surfaces 204A and 204B and the lower substrate 201 is 45 degrees. Therefore, when light Lp incident upon the reflective polarization layer 204 from a direction normal to the lower substrate 201 is such that a portion thereof (s wave) is reflected by an inclined surface 204A and travels towards a corresponding inclined surface 204B, and a portion thereof (p wave) passes through the inclined surface 204A and travels towards the lower substrate 201. The reflected portion of the light (s wave) is reflected by the inclined surface 204B, travels in the direction normal to the lower substrate 201, and is used for display. Light Ls incident upon the reflective polarization layer 204 obliquely from above the lower substrate 201 is similarly reflected by an inclined surface 204A and a corresponding inclined surface 204B in that order and exits from the reflective polarization layer 204 in a direction opposite to the incidence direction. Therefore, in order to cause a large amount of light to exit in a direction of a line of sight of a user, it is necessary for the direction of incidence of the light and the direction of the line of sight of the user to be the same. In such an arrangement, since outside light is caused to be incident upon the liquid crystal display device from behind the user, the incident light may be blocked by the user, thereby making the display darker.
The present invention has been achieved in view of the above-described circumstances. It is an object of the present invention to provide a liquid crystal display device which has excellent visibility and which realizes a bright display by increasing the amount of light reflected in a direction of a line of sight of a user in a reflective or a transflective liquid crystal display device.
It is another object of the present invention to provide an electronic device comprising the liquid crystal display device having the above-described excellent characteristics.